1. Field of the Invention
The present invention relates to an ink jet print head for use in an office or industrial environment, and also to a method of producing the ink jet print head.
2. Description of the Related Art
FIG. 1 is a cross-sectional view showing an example of a conventional ink jet print head. The ink jet print head includes an orifice plate 302 formed with a nozzle 301, a chamber plate 304 formed with a pressure chamber 303, a restrictor plate 306 formed with a restrictor 305, a diaphragm/filter plate 309 formed with a diaphragm 307 and a filter 308, a housing 311 formed with a common ink channel 310, a piezoelectric element 312, and a piezoelectric element fixing plate 313 for fixing the piezoelectric element 312 in place. The piezoelectric element 312 is made up of a number of plate-shaped piezoelectric material pieces and a number of electrodes alternately stacked one on the other. For the sake of brevity, the piezoelectric element will be hereinafter referred to simply as xe2x80x9cpiezoelectric elementxe2x80x9d.
The housing 311 includes edges X1 and Y1 for setting the position of the piezoelectric element fixing plate 313 in the X and Y directions, respectively. The piezoelectric element fixing plate 313 is abutted against and fixed to the edges X1 and Y1 by adhesive (not shown). The adhesive must be applied according to the machining precision of the positioning edges X1, Y1 and must be applied thinly.
However, in order to reduce variation in ink ejection, the diaphragm 307 and the piezoelectric element 312 need to be attached to each other with great positional accuracy. This requires that the housing 311 and the piezoelectric element fixing plate 312 be machined with extreme precision. For example, the distance from the positioning edge Y2 of the piezoelectric element fixing plate 313 to where the piezoelectric element 312 is adhered to the diaphragm 307 must be extremely precise so the positioning edges X1, Y1 must be machined in the housing 311 with extremely high precision. Also, the corners between various surfaces must be extremely close to perfect right angles. If not, the surface X1 adhered to the piezoelectric element fixing plate 313 will lean toward or away from the diaphragm 307, so that the surface of the piezoelectric element 312 that is adhered to the diaphragm 307 will also slant with regard to the diaphragm 307. Full and uniform contact between the adhered surfaces of the piezoelectric element 312 and the diaphragm 307 cannot be achieved.
If the adhesive layer is too thin or non-uniform, then the piezoelectric element fixing plate 313 cannot be adhered in accordance with the reference edges X1, Y1. As a result, the adhering surfaces of the diaphragm 307 and the piezoelectric element 312 will not contact each other uniformly, resulting in the diaphragm 307 and the piezoelectric element 312 being adhered to each other at a slant.
When the housing 311 and the piezoelectric element fixing plate 313 are made from different materials having different thermal expansion coefficients, then the ink jet head can suffer from warping if the piezoelectric element fixing plate 313 is fixed to the housing 311 by adhesive, for example. The warping can result in variations in ink ejection properties, especially at the end nozzles.
For these reasons, in order to reduce variation in ink ejection, the precision of all components and the thickness of the adhesive must be managed carefully. Components such as the housing 311 and the piezoelectric element fixing plate 313 must be made with high machining precision and so are expensive. As a result, the ink jet head is expensive to make.
In view of the foregoing, it is an object of the present invention to overcome the above-described problems and to provide an inexpensive ink jet print head with less positional shift between the piezoelectric elements and the diaphragm and reduced variation in ink ejection properties, and a method of manufacturing the ink jet print head.
In order to achieve the above-described objectives, an ink jet print head according to the present invention includes a pressure chamber portion with pressure chambers, an orifice plate, a restrictor plate, a diaphragm forming a side of the pressure chambers, stacked piezoelectric elements, a piezoelectric element fixing plate, and a housing. The orifice plate is formed with orifices in a one-to-one correspondence with the pressure chambers. Each orifice brings a corresponding pressure chamber into fluid communication with atmosphere. The restrictor plate is formed with ink channels in fluid communication with the pressure chambers. The stacked piezoelectric elements are attached to the diaphragm in a one-to-one correspondence with the pressure chambers. Each stacked piezoelectric element generates, through the diaphragm, a pressure fluctuation in a corresponding pressure chamber when applied with an electric signal. The piezoelectric element fixing plate is fixedly attached to and supports the stacked piezoelectric elements.
The housing includes a common ink channel portion and internal side walls. The common ink channel portion is formed with a common ink channel in fluid communication with the channels in the restrictor plate. The internal side walls adjoin the diaphragm at one side to define a space that is open at an end opposite from the diaphragm. The piezoelectric element fixing plate and the stacked piezoelectric elements are disposed at least partially in the space with a gap existing between the piezoelectric element fixing plate and the internal side walls that define the space.
According to a method of the present invention for producing an ink jet print head, first a piezoelectric element set, a front end set, and a dummy restrictor plate are prepared, not necessarily in this order.
The piezoelectric element set includes a piezoelectric element fixing plate and stacked piezoelectric elements. The stacked piezoelectric elements are attached to the piezoelectric element fixing plate with a predetermined positioning.
The front end set includes a pressure chamber portion, an orifice plate, a restrictor plate, a diaphragm, and a housing. The pressure chamber portion has pressure chambers with positioning that corresponds to positioning of the stacked piezoelectric elements on the piezoelectric element fixing plate. The orifice plate is formed with orifices in a one-to-one correspondence with the pressure chambers. Each orifice brings a corresponding pressure chamber into fluid communication with atmosphere. The restrictor plate is formed with ink channels in fluid communication with the pressure chambers. The diaphragm forms a side of the pressure chambers. The housing includes a common ink channel, a space, and positioning holes. The common ink channel is in fluid communication with the channels in the restrictor plate. The space is defined by internal side walls that adjoin the diaphragm at one side. The space is open at an open end thereof opposite from the diaphragm. The space is large enough to insert through the open end the stacked piezoelectric elements and the piezoelectric element fixing plate until the stacked piezoelectric elements contact the diaphragm while a gap is maintained between the side walls and the piezoelectric element fixing plate. The positioning holes are disposed with a predetermined positioning.
The dummy restrictor plate includes dummy chambers and positioning holes. The dummy chambers have positioning that corresponds to positioning of the pressure chambers in the pressure chamber portion. The positioning holes have positioning that corresponds to positioning of the positioning holes of the housing.
Once the piezoelectric element set, the front end set, and the dummy restrictor plate are prepared, the positioning holes of the dummy restrictor plate are mounting on positioning pins of a positioning jig. The positioning pins of the positioning jig have a fixed positioning that corresponds to the positioning of the positioning holes of the dummy restrictor plate.
Then, the stacked piezoelectric elements of the piezoelectric element set are aligned with the dummy chambers of the dummy restrictor plate while the piezoelectric elements are observed through the dummy chambers of the dummy restrictor plate.
Then, the dummy restrictor plate is removed from the positioning jig.
Then, the front end set is mounted on the positioning jig by mounting the positioning holes of the housing on the positioning pins of the positioning jig. Adhesive is coated on one of the diaphragm of the front end set and the piezoelectric elements of the piezoelectric element set.
Then, the positioning jig is used to move the front end set toward the piezoelectric element set, while maintaining alignment between the front end set and the piezoelectric element set, until the piezoelectric element set passes into the space and the diaphragm and the stacked piezoelectric elements contact each other.